bread top flops

hi all,

i am not sure if this is the right place to ask but i am having trouble with my bread machine bread. it rises beautifully. smells great when its cooking, tastes wonderful. but no matter how well it rises when it is finished the top has fallen and i am left with a one and a half pound loaf of bread with a dip at the top. can anyone tell me what i am doing wrong? thanks lydia